Image sensors often operate by acquiring a signal in pixels, each pixel producing a value indicative of the amount of light impinging on the pixel. That value is usually an analog value, but modern image sensors often output digital versions of the analog value. This necessitates use of an analog to digital converter to convert the analog signal to digital.
A common type of A/D converter is a successive approximation type A/D converter.
It is often also desired to carry out black level compensation in such an image sensor to reduce the noise and increase the dynamic range. Black level compensation can be done using digital signal processing, or analog signal processing. Each may have its own drawbacks. Digital signal processing may sacrifice the upper dynamic range of the signal. Analog signal processing may require an additional D/A converter.